This invention relates to polyurethane-urea dispersions, and to polyurethane-urea polymers prepared therefrom.
Dispersions of polyurethane-ureas polymers are well known to be useful in preparing coatings of various types. These coatings are generally characterized in having excellent chemical resistance, abrasion resistance, toughness and other desirable properties.
These dispersions generally comprise a continuous phase, preferably aqueous but sometimes consisting of organic compounds, in which a polyurethane-urea polymer is dissolved or dispersed as a plurality of small particles. The polyurethane-urea polymer is generally the reaction product of an amine curing agent and an isocyanate-terminated prepolymer. The prepolymer is generally a reaction product of a relatively high equivalent weight polyol and a polyisocyanate. Sometimes the the prepolymer is modified to contain ionic groups in order to improve its dispersability in the continuous phase.
Although these dispersions provide otherwise excellent coatings, in some applications it is desirable to provide a coating which is electroconductive or static dissipative. Conventional polyurethane-urea coatings, despite the presence of ionic groups, have not proven sufficiently static dissipative to meet this requirement.
Because of the nature of polyurethane-urea coatings conventional antistatic agents are either not suitable, or are prohibitively expensive. Electroconductive fillers and fibers, which are often used in preparing bulk polymers, cannot be practically incorporated into coatings. Topical antistatic agents must be applied in an additional manufacturing step after the coating is applied and cured, which substantially increases manufacturing costs. Moreover, these topical additives are humidity dependent and tend to wear off during use. Other antistatic agents often are useful only in large quantities, which often causes the coating to lose important physical properties.
It is therefore desirable to provide a polyurethane-urea dispersion which is useful to form a static dissipative coating.